This invention relates to a detector for detecting a mechanical displacement such as a linear displacement or a rotation angle, and more particularly to, a detector of this kind of detector utilizing magnetism.
There exists a mechanical detector for detecting a mechanical displacement. In the mechanical detector, the whole parts from a moving part which moves corresponding to an object to be detected to a displaying member as a pointer are connected to each other by mechanical parts. However, this kind of mechanical means is complex in structure, and lacks durability because of an abrasion of the inner mechanisms due to their use. Thus, a non-mechanical displacement detector, such as an optical type detector, an electrical type detector and a magnetic type detector, has been used.
In the optical type detector, a light emitting element and a light receiving element are disposed so as to face each other, and a circular plate having a slit is disposed between the light emitting element and the light receiving element so that the circular plate can rotate. A displacement is converted into pulse signals generated by the rotation of the circular plate to count the number of the pulse signals which represent a displacement amount. However, since users wish to set the relationship between one pulse interval and the displacement amount, it is required to prepare various circular plates each having a slit to cope with various requirements of such users, which does not meet a mass production.
The electric type detector includes an electrostatic type detector and a potentiometer type detector. The electrostatic type detector is, in a word, a kind of variable capacitor which requires an operation for balancing an alternating-current bridge. Thus, the electrostatic type detector is not practical. On the other hand, in the potentiometer type detector, since the influence due to an abrasion of a sliding resistance is larger than the influence due to an abrasion in a pure mechanical device, the potentiometer type detector is unstable and lacks durability.
In the magnetical type detector, a distance between a pole of a permanent magnet and a magnetic sensor is changed and the linear range of the relationship between the displacement and the output of the magnetic sensor is narrow. For example, in a case where an output of the magnetic sensor is obtained by rotating a magnet in accordance with a displacement, the output varies in the form of a sine curve. Therefore, the measuring range is limited within approximately xc2x145 degrees if the linear range of the sine curve is utilized.
The present invention belongs particularly to a non-mechanical displacement detector utilizing magnetism among the aforementioned non-mechanical type detectors. The present invention is to provide a displacement detector which solves problems of the aforementioned conventional devices and has characteristics that the displacement detector is simple, stable and endurable, and can output various types of signals, including analog and/or digital signals.
According to the present invention, a magnetic plate having a thickness which changes along a single line in accordance with the distance from one end of the magnetic plate, i.e., a magnetic plate with tapered thickness, is magnetized in a direction of its thickness. A magnetic sensor is disposed near the surface of the magnetic plate so that it can move relative to the magnetic plate in the tapered direction of the plate thickness while keeping a constant distance therebetween, to detect the magnetic field strength on the surface of the magnetic plate. A drive mechanism for conducting the aforementioned relative movement of the magnetic sensor and the magnetic plate is set such that the drive mechanism moves in accordance with the movement of an object to be detected. The magnetic sensor outputs a displacement detect signal.
The aforementioned xe2x80x9csingle linexe2x80x9d used in the sentence, xe2x80x9ca magnetic plate having a thickness which changes along a single line in accordance with the distance from one end of the magnetic plate,xe2x80x9d denotes a straight or circular line. The aforementioned xe2x80x9crelative movement of the magnetic sensor and the magnetic plate in the tapered direction of the plate thicknessxe2x80x9d denotes a linear displacement or a rotational displacement along the aforementioned line.
Furthermore, a correction means for correcting a change of magnetic force and output of the magnetic sensor due to temperature change is provided in the aforementioned device. This means includes a temperature correction means for conducting temperature correction by comparing an output of one or a plurality of magnetic sensors fixed to the magnetic plate with a reference value or utilizing a relationship between the outputs, a temperature correction means for conducting a temperature correction by utilizing an output of a magnetic sensor disposed so as to touch a magnet disposed apart from the magnetic plate, and a temperature correction means for conducting a temperature correction by utilizing an output of the magnetic sensor, which is movable relative to the magnetic plate, at a predetermined position.